Relay switches having physically movable contact elements are used in many different applications. In particular, it is common to use a relay switch having physically movable contact elements in order to switch resistors and/or capacitors into or out of an attenuator network, in order to vary the effective attenuation factor of the network. However, since movable contact elements are used, there is the possibility of contamination degrading the electrical contact provided by a relay switch. It is therefore desirable that such a relay switch be hermetically sealed to prevent contamination. However, sealing generally makes actuation of the relay switch difficult.
It is well known to use magnetic forces for bringing about movement of the contact element of a relay switch. In one kind of relay switch, the contact element is carried by an armature that also carries a permanent magnet. The armature is mounted on a support member so as to be pivotable about an axis that lies between the North and South poles of the permanent magnet between two end positions. In a first of these end positions, the North pole of the permanent magnet is at a minimum distance from the support member and the South pole is at a maximum distance, and vice versa in the second end position. Two small bodies of thermal compensation material are positioned on the support member, so as to be as close as possible to the North and South poles respectively. An electrical resistance heater is in thermally-conductive contact with each body of thermal compensation material. The thermal compensation material is a soft ferromagnetic material at room temperature (about 18 degrees C.) and upon heating above its Curie point (about 85 degrees C.) the thermal compensation material changes from being ferromagnetic to diamagnetic. In a first stable state of this known relay switch, the armature is in its first end position and so the North pole of the permanent magnet is at a minimum distance from its associated body of thermal compensation material and the South pole is at a maximum distance, and in a second stable state the armature is in its second end position and the North and South poles are at maximum and minimum distances respectively from the associated bodies of thermal compensation material. So long as the two bodies of thermal compensation material remain ferromagnetic, the switch remains in its first or second stable state. If the switch is in its first stable state, and the body of thermal compensation material associated with the North pole is heated above its Curie point, the attraction of the South pole to its associated body of thermal compensation material overcomes the attraction of the North pole, and the switch will toggle to its second stable state. The switch can then be returned from its second stable state to its first stable state by heating the body of thermal compensation material associated with the South pole.
In this known thermomagnetic relay switch, the armature is mounted to the support member by means of a pivot mechanism having two rigid elements that undergo relative rotational movement when the armature pivots from one stable state to the other stable state. Friction and stiction between the two rigid elements affect the mechanical properties of the pivot mechanism.
U.S. Pat. No. 4,150,420 discloses a cam-actuated switch comprising a metal contact element bonded to a body of elastomeric material. The body of elastomeric material is carried by a cam follower that is mounted in cantilever fashion to a circuit board. A rotatable cam engages the cam follower, and during the dwell of the cam the metal contact element is pressed into contact with two conductor runs of the circuit board and establishes electrical connection between these conductor runs. This type of switch has good high frequency electrical performance, but suffers from the disadvantage that it is necessary to rotate the cam in order to actuate the switch.